Welcome to the Electrical Equipment Troubleshooting and Maintenance Module
This document is intended as a general informational guide only.
Before performing any work or purchasing any equipment you should consult your electrical engineer, electrician or an electrical consultant.
ElectricalDM is not responsible for misinterpretation or misuse of this information.
Equipment Maintenance Troubleshooting
Troubleshooting is a form of problem solving, often applied to repair failed products or processes on a machine or a system. It is a logical, systematic search for the source of a problem in order to solve it, and make the product or process operational again.
To expertly troubleshoot electrical equipment, problems must be solved by replacing only defective equipment or components in the least amount of time. One of the most important factors in doing this, is the approach used. An expert troubleshooter uses a system or approach that allows them to logically and systematically analyze a circuit and determine exactly what is wrong.
Troubleshooting is a systematic approach to problem solving that is often used to find and correct issues with complex machines, electronics, computers and software systems. The first step in troubleshooting is gathering information on the issue, such as an undesired behavior or a lack of expected functionality. Other important information includes related symptoms and special circumstances that may be required to reproduce the issue.
Reserved for EDM Paid Subscritpion
Reserved for EDM Paid Subscritpion
Motor Maintenance Troubleshooting
| Motor Fails to Start Upon Initial Installation | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Motor is wired incorrectly | Motor should be rewired correctly | ---- | ||||
| Motor damaged and rotor is striking stator | Rotate the motor’s shaft and feel for surface rubbing or rough spots. | May be able to reassemble; otherwise, motor should be replaced. | ||||
| Power supply or line trouble | Check the source of power, overload, fuses, controls, etc. | ---- | ||||
| Motor Has Been Running, Then Fails to Start | ||
|---|---|---|
| Cause | Solution | Notes |
| Fuse or circuit breaker is tripped. | Replace the fuse or reset the breaker. | - |
| Stator is shorted or went to ground. (Motor will make a humming noise and the circuit breaker or fuse will trip). | Check for leaks through the coils. If leaks are found, the motor must be replaced. | - |
| Motor overloaded or jammed. | Inspect to see that the load is free. Verify the amp draw of motor versus the nameplate rating. | - |
| No voltage supply. | Check feed connections to control system and from control to motor. | - |
| Low voltage supply | Check voltage supply and ascertain that voltage remains within 10% of the rated voltage shown on the motor nameplate. | - |
| Loose connection at some terminal lug. | Tighten all connections. | - |
| Brushes | Brushes may be worn, dirty or incorrectly fitted. | - |
| Capacitor (on single phase motor) may have failed. | First discharge the capacitor then test the capacitor. | - |
| Motor Runs but Slows Down | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Voltage drop. | If the voltage is less than 90% of the motor’s rating, contact your power company or check to see that another piece of equipment isn’t taking power away from the motor. | - | ||||
| Load increased. | Verify that the load has not changed or the equipment has not tightened. If it is a fan application, verify that the air flow hasn’t changed. | - | ||||
| Motor Takes Too Long to Accelerate | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Defective capacitor. | First discharge the capacitor then test the capacitor. | - | ||||
| Bad bearings. | Noisy or rough feeling bearings should be replaced by the motor supplier. | - | ||||
| Voltage too low. | Make sure the voltage is within 10% of the motor’s nameplate rating. If not, contact your power company or check if some other equipment is power away from the motor. | - | ||||
| Motor controller not properly set. | Adjust the acceleration trim pot of the controller. | - | ||||
| Brushes are worn. | Verify brush length. | - | ||||
| Bearings may be defective. | Inspect bearings. Noisy or rough bearings should be replaced. | - | ||||
| Motor Runs in the Wrong Direction | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Incorrect wiring. | Rewire the motor according to the schematic provided with the motor. | - | ||||
| Motor Overloaded/Thermal Protector Continuously Trips | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Load too high. | Verify that the load is not jammed. If the motor is a replacement, verify that the rating is the same as old motor. If the previous motor was a special design, a stock motor may not be able to duplicate the performance. Remove the load from the motor and inspect the amp draw of the motor unloaded. It should be less than the full load rating stamped on the nameplate (only true for three phase motors). | - | ||||
| Ambient temperature too high | Verify that the motor is getting enough air for proper cooling. Most motors are designed to run in an ambient temperature of or less than 40°C. (Note: A properly operating motor may be hot to the touch.) | - | ||||
| Motor Overheating | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Overload. Compare actual amps (measured) with nameplate rating. | Locate and remove the source of excessive friction in the motor or load. Reduce the load or replace the motor with one of greater capacity. | - | ||||
| Single phasing (three phase only). | Check the current at all phases. It should be approximately the same. | - | ||||
| Improper ventilation. | Check external cooling fan to be sure air is moving properly through the cooling channels. If there is excessive dirt build-up, clean the motor. | - | ||||
| Unbalanced voltage (three phase only). | Check the voltage at all phases. It should be approximately the same. | - | ||||
| Rotor rubbing on stator. | Tighten the thru bolts. | - | ||||
| Over voltage or under voltage. | Check the input voltage at each phase of the motor to make sure the motor is running at voltage specified on the nameplate. | - | ||||
| Open stator winding (three phase only). | Check the stator resistance at all three phases for balance. | - | ||||
| Improper connections. | Inspect all the electrical connections for proper termination, clearance, mechanical strength,and electrical continuity. Refer to the motor lead diagram.. | - | ||||
| Motor Vibrations | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Motor misaligned to load. | Realign the load. | - | ||||
| Load out of balance (direct drive application). | Remove the motor from load and inspect the motor by itself. Verify that the motor shaft is not bent. | - | ||||
| Defective motor bearings. | Test the motor by itself. If the bearings are bad, you will still hear noises or feel for roughness. | - | ||||
| Load too light (single phase only). | Some vibration at a light load is standard. Consider switching to a smaller motor for excessive vibration. | - | ||||
| Defective winding. | Test the winding for shorted or open circuits. The amps may also be high. For defective winding, replace the motor. | - | ||||
| High voltage. | Check the power supply to make sure voltage is accurate. | - | ||||
| Bearings Fail | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Load to motor may be excessive or unbalanced. | Check the motor load and inspect the drive belt tension to ensure it’s not too tight. An unbalanced load will also cause the bearings to fail. | - | ||||
| High ambient temperatures. | If the motor is used in an environment with high ambient temperatures, a different type of bearing grease may be required. You may need to consult the factory. | - | ||||
| High motor temperatures. | Check and compare the actual motor loads to the motor’s rated load capabilities. | - | ||||
| Capacitor Fail | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Ambient temperature too high. | Verify that the ambient temperature does not exceed the motor’s temperature rating (found on the nameplate). | - | ||||
| Possible power surge to the motor. | If this is a common problem, install a surge protector. | - | ||||
| Harmonics | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Some electrical loads (such as computers, controls, drives, and energy-saving lighting systems) can cause other frequencies to appear in your measurements. These other frequencies, which are multiples of the fundamental ( 50 or 60Hz) (so 120 Hz, 180 Hz, and so on for a 60 Hz fundamental frequency), are called harmonics. | Motor drives can be affected by harmonics, they are often the source of harmonics that affect other devices in the facility.You may need to consider adding filtering to block those harmonics. | - | ||||
| Transients | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Transients can damage motors and other parts of the motor circuitry. | You may need to consider adding surge protection to block those transients. | - | ||||
| High Noise Level | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Unbalance. | Vibrations can be eliminated by balancing rotor. If load is coupled directly to motor shaft, the load can be unbalanced. | - | ||||
| Distorted shaft. | Shaft can be bent; check rotor balance and eccentricity. | - | ||||
| Incorrect alignment. | Check motor alignment with machine running. | - | ||||
| Uneven air gap. | Check shaft for warping or bearing wear. | - | ||||
| Dirt in the air gap. | Dismantle motor and remove dirt or dust with jet of dry air. | - | ||||
| Extraneous matter stuck between fan and motor casing. | Dismantle motor and clean. Remove trash or debris from motor vicinity. | - | ||||
| Loose motor foundation. | Tighten all foundation studs. If necessary, realign motor. | - | ||||
| Worn bearings. | Check lubrication. Replace bearing if noise is excessive and continuous. | - | ||||
| Overheating of bearings | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Excessive grease. | Remove grease bleeder plug and run motor until excess grease is expelled. | - | ||||
| Excessive axial or radial strain on belt. | Reduce belt tension. | - | ||||
| Incorrect alignment. | Check motor alignment with machine running. | - | ||||
| Deformed shaft. | Have shaft straightened and check rotor balance. | - | ||||
| Rough bearing surface. | Replace bearings before they damage shaft. | - | ||||
| Loose or poorly fitted motor end shields. | Check end shields for close fit around circumference and tightness. | - | ||||
| Lack of grease. | Add grease to bearing. | - | ||||
| Hardened grease cause locking of balls. | Replace bearings. | - | ||||
| Foreign material in grease. | Flush out housings and relubricate. | - | ||||
| Intense Bearing Vibration | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Unbalanced rotor. | Balance rotor statically and dynamically. | - | ||||
| Dirty or worn bearing. | If bearing rings are in perfect condition, clean relubricate the bearing, otherwise replace bearing. | - | ||||
| Bearing rings too tight on shaft and/or bearing housing. | Before altering shaft or housing dimensions, it is advisable to ascertain that bearing dimensions correspond to manufacturer's specifications. | - | ||||
| Extraneous solid particles in bearing. | Take bearing apart and clean. Reassemble only if rotating and support surfaces are unharmed. | - | ||||
| Slip Ring Motor Operating at Low Speed with External Resistance Disconnected | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Control circuit conductors too light. | Install heavier conductors on control circuit. | - | ||||
| Control too far from motor. | Bring control closer to motor. | - | ||||
| Open circuit on rotor circuits (including connections with control apparatus). | Test circuit with a magneto, or other means, and undertake necessary repairs. | - | ||||
| Dirt between brush and slip ring. | Clean slip rings and insulation assembly. | - | ||||
| Brushes gripe on brush holders. | Select brushes of correct size. | - | ||||
| Incorrect pressure on brushes. | Check pressure on each brush and adjust it accordingly. | - | ||||
| Rough surfaces on slip rings. | File, sand and polish. | - | ||||
| Eccentric rings. | Machine on lathe or with portable tool without removing from machine. | - | ||||
| High current density on brushes. | Reduce load or replace brushes. | - | ||||
| Poorly set brushes. | Reset brushes correctly. | - | ||||
| Brush Sparking | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| Poorly set brushes with insufficient pressure. | Check brush setting; adjust for correct pressure. | - | ||||
| Overload. | Reduce load or install motor with higher capacity. | - | ||||
| Slip rings in poor condition. | Clean rings and reset brushes. | - | ||||
| Oval slip rings. Rough surfaces and scored rings. | Polish the slip rings with an emery and machine the same on lathe. | - | ||||
| Excess of Vibration. | Balance the rotor, check the brushes for free movement within holders. | - | ||||
| Motor stalls | ||||||
|---|---|---|---|---|---|---|
| Cause | Solution | Notes | ||||
| One phase may be open. | Check supply lines for open phase. | Stalling protection: When the motor is unable to start because of the overload or motor stalls when running, it draws locked rotor current from the supply. It is essential to disconnect the motor as early as possible under this condition to avoid damage to the machine. A protective device should be arranged to disconnect the motor if the current continues for longer than normal starting time (about 10 seconds). | ||||
| Wrong application. | Change type or size. Consult motor manufacturer. | - | ||||
| Overload. | Reduce load. | - | ||||
| Low voltage. | Check that nameplate voltage is maintained. Check connection. | - | ||||
| Open circuit. | Fuses blown. Check overload relay, stator and push buttons. | - | ||||
Power Transformer Maintenance Troubleshooting
Select Transformer Problem
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Power Breaker Maintenance Troubleshooting
Select SF6 Breaker Problem
Select Miniumn Oil Breaker Problem
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Battery Bank Troubleshooting
Select Battery Bank Problem
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